Quick acting miniature electric fuses have been widely used in various electric and electronic circuits. In most of these fuses, the fusible element is either soldered to the ends of the lead wires or it is simply secured thereto mechanically.
One type of miniature fuse is described in U.S. Pat. No. 3,227,841, issued to Aldens J. Gaia on Jan. 4, 1966. This fuse comprises a hollow housing made of an insulating material such as a refractory material, an electrically non-conductive disc also made of a refractory material and mounted in said housing and a pair of electrically conductive terminals extending through a pair of spaced openings in said disc mounting. The two terminals are partially enclosed in the housing and a fusible conductor stretches between the enclosed ends of said terminals and is soldered thereto at both ends.
Another type of fuse comprises a housing which includes a base made of an insulating material and a pair of lead wires passed thorugh the base partially into the housing. Each tip of the lead wires is bent and a fusible conductor stretches between these tips with the ends of the fusible elements secured to the respective tips of the lead wires by means of an electrically conductive paste. This type of fuse is described in Japanese Utility Patent 43-7710.
These prior fuses, however, are extremely unstable since the length of the fusible element is subject to variations, and evaporation of the electrodes due to arcing heat tends to prolong the arcing time. Accordingly, these fuses have not been entirely satisfactory.
In another type of fuse which is described in British Pat. No. 969,654, published on Sept. 16, 1964, the fuse comprises an integral fuse body through which extends a pair of spaced lead wires projecting beyond opposite ends of the fuse body, and a fusible element between the two ends of the lead wires in the fuse body. The fusible element and the lead wires are wholly embedded in a solid, arc-quenching filler made of epoxy resin and an imperforate cup-shaped cap is fitted over the fuse body to encase the fusible element, the lead wire portions in the fuse body and the epoxy resin filler.
The difficulty with fuses using epoxy fillers, however, is that, the heat generated by the passage of electric current causes thermal expansion with subsequent contraction when current flow is interrupted. Repeated thermal expansions and contractions often cause breakdown of the fusible element.
Accordingly, it is an object of this invention to provide a micro-fuse which is substantially free from the aforesaid inherent drawbacks of the prior fuses.
It is a further object of this invention to provide a micro-fuse which is quick acting and has improved arc-extinguishing characteristic.
It is also an object of this invention to provide such a fuse which also exhibits improved stability and thermal capacity.
The foregoing and other objects of this invention will be described in detail in the ensuing description of the preferred embodiment of the invention taken in conjunction with the accompanying drawings.